(a) Field of the Invention
The present invention relates to a catalyst composition, and a method for preparing the same, and a method for preparing polyolefin using the same. More specifically, the present invention relates to a catalyst composition comprising a dinuclear metallocene compound with a novel structure, which can prepare polyolefin with high molecular weight, a method for preparing the same, and a method for preparing polyolefin using the same.
(b) Description of the Related Art
Since a Zeigler-Natta catalyst widely applied in an industrial process is a multi-site catalyst, the molecular weight distribution of the produced polymer is wide, and the composition distribution of comonomers is not uniform, and thus, has a limitation in securing desired properties.
Meanwhile, a metallocene catalyst is a single-site catalyst having one kind of an active site, and it has advantages in that the molecular weight distribution of the produced polymer is narrow, and that the molecular weight, stereoregularity, crystallinity, particularly reactivity of comonomers may be greatly controlled according to the structure of the catalyst and the ligand. However, polyolefin polymerized using a metallocene catalyst has narrow molecular weight distribution, and if applied for some products, productivity is remarkably decreased due to extrusion load and the like, rendering site application difficult, and thus, there have been many attempts to control the molecular weight distribution of polyolefin
For this, a method of using a mononuclear metallocene compound and a dinuclear metallocene compound is known.
As an example of the mononuclear metallocene compound, U.S. Pat. No. 5,032,562 describes a method of preparing a polymerization catalyst by supporting two different transition metal catalysts on one carrier. This is a method of producing bimodal distribution polymer by supporting a titanium (Ti)-based Ziegler Natta catalyst producing high molecular weight and a zirconium (Zr)-based metallocene catalyst producing low molecular weight on one carrier, however, it has disadvantages in that the supporting process is complicated, and the morphology of polymer becomes worse due to a cocatalyst.
And, studies on changing copolymer selectivity and activity of a catalyst in copolymerization using a dinuclear metallocene compound has been reported, and in case of some metallocene catalysts, copolymer incorporation and activity increase have been reported.
For example, Korean Patent Application No. 2003-12308 discloses a method of controlling molecular weight distribution by supporting a dinuclear metallocene catalyst and a mononuclear metallocene catalyst on a carrier together with an activator and polymerizing while changing the combination of catalysts in the reactor. However, this method has a limitation in simultaneously realizing the properties of each catalyst, and has a disadvantage in that a metallocene catalyst part is dissociated in the carrier component of the final catalyst, thus causing fouling of a reactor.
And, a synthesis method of a Group 4 metallocene catalyst having a biphenylene bridge and polymerization of ethylene and styrene using the same have been reported (Organometallics, 2005, 24, 3618). According to this method, it is stated that the catalytic activity is high and the molecular weight of the obtained polymer is high, compared to a mononuclear metallocene catalyst. It has been also reported that the reactivity of a catalyst may be changed by converting the bridge structure of Group 4 dinuclear metallocene catalyst (Eur. Polym, J. 2007, 43, 1436).
However, if using these methods, previously reported Group 4 metallocene catalyst having a biphenylene bridge has problems in terms of addition of substituents and modification of a structure. Therefore, there is a need for development of novel metallocene catalyst useful for preparation of olefin.